Significance of pulmonary input impedance in right ventricular performance.

Right ventricular adaptation to changes in pulmonary input impedance was studied in open-chest dogs. When identical increases in pulmonary vascular resistance are imposed by two different manoeuvres (lung inflation and clamping of the left pulmonary artery), external power and pressure-time integral of the right ventricle at similar filling pressure are always greater during clamping than during inflation. Further studies demonstrate that, at equal increases in pulmonary input impedance modulus at 0 Hz, the clamping produces a greater change in the sum of the first three harmonics of impedance than the inflation (respectively +77% and -10% vs control modulus; -82% and +8% vs control phase). These impedance changes could explain the different behaviour of the right ventricle either by better matching of the ventricular internal impedance or by functional modification of the outflow tract.